Gas Tank pressure

[ScottyWM]

Had an odd occurance I'm wondering if anyone else has experienced. About a month ago I had to add gas to my wagon. Undid the gas cap and had a rather strong expulsion of air/vapors/spittle from the filler neck. Thought that was odd, but since I had run it down to almost empty, thought it might just be due to there being so little gas in the tank (running on fumes). But, I continued to have this experience for a number of fill-ups, maybe about 3-4. Then, I thought to myself, I'll check it once or twice a day whether I've run the car or not and see if it seems to stay pressurized. Of course then it stopped having this condition. And now for the last couple weeks, there has been no observed abnormal pressure when I remove the gas cap.

Time for a new gas cap or what?

[shogun]

pressure or vacuum? There were some real problems on E38 that even the tanks collapsed due to vacuum build up. Check the tank airation system

[ScottyWM]

pressure or vacuum? There were some real problems on E38 that even the tanks collapsed due to vacuum build up. Check the tank airation system

Yeah, I was thinking vacuum at first too. But no, it was definately blowing out, not sucking in.

[glen-sj]

start by checking into the fuel vent system, perhap there some blockage. There is a expansion tank and a chacoal canister in the vent system.
http://www.realoem.com/bmw/showparts.do?model=HD63&mospid=47404&btnr=16_0103&hg=16&fg=10

[bimmerd00d]

start by checking into the fuel vent system, perhap there some blockage. There is a expansion tank and a chacoal canister in the vent system.
http://www.realoem.com/bmw/showparts.do?model=HD63&mospid=47404&btnr=16_0103&hg=16&fg=10

Also, if you can't find this, it's inside the passenger wheel liner...I watched Scott H and a handful of guys replace a tank a few years ago and i had no idea that was even there :)

[ScottyWM]

Also, if you can't find this, it's inside the passenger wheel liner...I watched Scott H and a handful of guys replace a tank a few years ago and i had no idea that was even there :)

Thanks guys, I assume that is inside the rear passenger wheel well. As the problem seems to have corrected itself, I'll probably put this off for a while. It may be that it got clogged, then blew it out or blew off a hose or something.

[bimmerd00d]

Thanks guys, I assume that is inside the rear passenger wheel well. As the problem seems to have corrected itself, I'll probably put this off for a while. It may be that it got clogged, then blew it out or blew off a hose or something.

It happens to my E34 wagon, happened to my old E34, happens to my E39 540i too. It seems to come and go with temperature. It will only do it on the hottest of days with the wagon.

[genphreak]

Seen it on and off without detriment on many cars, inc all my e34s (but not very often). Happens when the tank is fairly empty and has warmed up quickly (pressure) or if it has cooled down (vacuum).